Question about Single Sided Serial board

Projects General Guidance
1

Greetings,

I have been looking into this board, and there are few things that are really bothering me, and i would love to get them explained by you.

  1. In this updated version, there is an inductor L1 between AVCC and VCC. Why on the earth that has been done?
  2. There also is a capacitor C9 in the transmit circuit, but its facing wrong direction in the schematic. Oh, i think i just lost my rely on this scheme.
  3. A crystal needs two capacitors to its each terminal. Any size i have tried between 18pF-22pF seems to be ok. How accurate is this need of 22pF, or is it just the recommendation, if so, where to it leads to use 18pF instead of the recommended (suggested) 22pF ?

Thank you so much for caring, also if you can guide me in this somehow; please do.

With best regards, freezE

2
  1. In this updated version, there is an inductor L1 between AVCC and VCC. Why on the earth that has been done?

To add decoupling for the analogue side.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

  1. Yes C9 appears to be the wrong way round on the schematic.

  2. How accurate the capacitors need to be depends on the crystal. The main problem with getting the value wrong is that it will just not start oscillating. It also affects very slightly the frequency it oscillates at but this is insignificant in the context of this circuit application.

3

Thanks for your reply!

Now that De-Coupling thing is getting interesting. I haven't learned much about inductors, in the de-coupling even less if anything, so i think i need a little more specified explaining how that works in this case. I couldn't dig it up from the site.

So what will exactly happen if i have it there, and what will happen if i don't have it there ?

MODIFY: Oh, i have 100uH 350mA leaded inductors. Is that suitable for the usage?

With best regards, freezE

4

The useof an inductors shown in the last diagram of that pages linked to.
An inductor looks like a high impedance to high frequencies and a low resistance to DC, so it stops ripple getting in to the analogue side. Useing it gives you more stable readings from the A/D converter.
Yes any inductor value is better tan nothing. In general the higher value the better.

5

Sweet, thanks Mike, you are awesome.

You mentioned the bigger value, so i suppose that value was the H value not the maximum current? Although, the bigger the current is, more it can take and therefore the component is better that way as well right ?

6

The H value is the inductance in Henries

It has nothing to do with the current rating which is mainly determined by the gauge of wire used for the coil and the magnetic saturation capacity of the core it is wound on.
In this situation the current is tiny and there is no advantage in having a bigger current rated coil.